1. Field of the Invention
The present invention relates to an electrostatic copying apparatus of a type in which a tone image or an electrostatic latent image corresponding to an original document and formed on a surface of a photosensitive member is transferred onto a transfer paper such as a copy paper and the like, and more particularly, to a control system for controlling the movement of a movable portion of an optical system intended to form the image of the original document on the photosensitive member through exposure, or the movement of an original support table, and also for controlling the cleaning operation by a cleaning device which is arranged to carry out the cleaning operation through removal of toner or electrical charge remaining on the surface of the photosensitive member after transfer.
2. Description of the Prior Art
In some conventional transfer type electrostatic copying apparatuses, the moveable portion of an optical system for forming through exposure an electrostatic latent image corresponding to an original document on a photosensitive drum, which is constructed by providing a photosensitive layer on the outer periphery of a drum, is located at a home or initial position when copying is not carried out. Adjacent to the outer periphery of the photosensitive drum, there is provided cleaning means which removes the residual toner remaining on the photosensitive layer, and the photosensitive layer thus is cleaned as the photosensitive drum rotates. For carrying out a copying operation, it is preferable to first clean the surface of the photosensitive drum and then effect the exposure. For this purpose, when a print button is depressed for the copying operation, the photosensitive drum first starts rotating and simultaneously, the copy paper begins to be fed, but the movable portion of the optical system reamains stationary. Upon rotation of the photosensitive drum more than one time, the photosensitive layer of the photosensitive drum is to be cleaned over its entire peripheral surface. In the state where the above cleaning has been completed, the movable portion of the optical system starts moving thereby to effect the exposure and development, and thus, the image of the original document is copied onto the copy paper being continuously transported. In the conventional arrangement as described above, the presence is inevitable of the time period during which the movable portion of the optical system is at rest up to the effecting of the cleaning of the photosensitive layer for the photosensitive drum after the depression of the print button for the copying operation. Accordingly, from the viewpoint of reducing the time required for copying, omission of the cleaning time before the copying operation is strongly desired.
Furthermore, in the prior art transfer type electrostatic copying apparatus as described above, when a plurality of copies are to be made successively, it is so arranged that, regarding the copy paper sheets after a second sheet, copy paper sheet to be subjected to subsequent copying operation is fed when the movable portion of the optical system is on its way back to the home position after completion of the exposure for the previous copying process, whereby reduction of the copying time for the copy paper sheets after the second sheet is intended. The prior art arrangement has a disadvantage in that, since the transportation starting timing for the first copy paper sheet immediately after depression of the print button and the starting timing for the copy paper sheets after the second copy paper sheet differ from each other, the construction of the copy paper transportation control is undesirably complicated.
Moreover, in the conventional transfer type electrostatic copying apparatus, the exposure onto the photosensitive layer of the photosensitive drum is arranged to be effected simultaneously with the starting of the movable portion of the optical system, and therefore, in a transient time period during which the movable portion is brought from the stationary state to the running state at a predetermined speed suitable for exposure, there is a possibility that the image corresponding to the original document and formed on the photosensitive layer of the photosensitive drum is blurred, with the result that the image of the original document to be formed on the copy paper is made indefinite.
For preventing such blur in the image at an initial stage of movement of the movable portion of the optical system, it is necessary to preliminarily move the movable portion so that it is brought into the running state at a speed suitable for exposure. By operating in the above described manner, the moving distance of the movable portion must be made longer, thus resulting in a large size of the structure.
Accordingly, it is a primary object of the invention to provide a transfer type electrostatic copying apparatus in which reduction of the copying time is possible.
It is another object of the invention to provide a transfer type electrostatic copying apparatus of the above described type in which the contruction of the transportation control of the transfer paper such as copy paper is simplified.
It is a further object of the invention to provide a transfer type electrostatic copying apparatus of the above described type which is compact in size and capable of achieving definite and clear copies.
In a typical prior art copy paper feeding device, the copy paper sheet at the top of the stack of copy paper sheets is caused to contact the copy paper feeding roller under pressure by elastically urging upwardly the mounting plate of a copy paper cassette in which the copy paper sheets are placed through spring means. In this prior art arrangement, if the size of the copy paper sheets is comparatively large with a consequent heavy weight, the pressure contact force between the copy paper feeding roller and the copy paper sheet at the top of the stack is small, while in the case where the size of the copy paper sheet is relatively small with a consequent light weight, the pressure contact force therebetween tends to be large. In other words, the pressure contact force between the copy paper feeding roller and the copy paper sheet at the top of the stack differs according to the sizes of the copy paper sheets, and consequently according to the weights of the copy paper sheets. Therefore, there are such disadvantages that a plurality of copy paper sheets are fed simultaneously or the copy paper sheets are positionally deviated with respect to the transporting direction so as to be fed in an undesirable slanted orientation.
It is an object of this invention to provide a copy paper feeding device for a copying apparatus for feeding out copy paper sheets from a copy paper feeding cassette positively one sheet at a time.
In an electrostatic copying apparatus which is arranged to develop an electrostatic latent image formed on a photosensitive plate by employing a mixture of toner and carrier as a developing material, there is a tendency that, as many sheets of copies are made, only the toner is consumed, with its presence in the developing material being gradually decreased, and thus, favorable copied images can not be obtained due to reduction of image density on the copy paper. Therefore, it becomes necessary to replenish the developing material with toner equivalent in amount to the toner consumed.
Although the preferable content of toner in the developing material varies depending on the electrical and physical properties of toner and carrier, the content should generally be in the region of approximately 3 to 5 weight %, and if the content is smaller than this level, reduction in the image density takes place, while on the other hand, if the content is larger than the above level, the phenomenon generally referred to as fogging is brought about due to adhesion of the toner to non-image formed portions on the photosensitive plate, with a marked reduction in the image quality. Accordingly, it is required to precisely control the amount of toner to be replenished according to the copying operation.
Furthermore, the amount of toner to be consumed tends to appreciably vary according to the kinds of original documents to be copied, for example, original documents only with letters, those having many black portions, etc. or by the sizes of the documents. Accordingly it is necessary to adjust the replenishing amount of toner at each time.
Prior art toner replenishment control devices employed for the above purpose have such construction that, a toner replenishing roller provided at an opening formed at the lower portion of a toner replenishing container and having undulation or convex and concave portions on its peripheral surface is driven for rotation depending on necessity for supplying the toner accommodated in the toner replenishing container into a developing device. In the above arrangement, the driving force for the toner replenishing roller is normally transmitted thereto from a driving unit of the copying apparatus or an exclusive roller through mechanical control means. More specifically, the type conventionally employed for the above purpose in many cases has been such that, at each copying process, the rotational force transmitted from the driving unit is controlled as desired through a ratchet mechanism and the like so as to be transmitted to the toner replenishing roller for rotating said roller. However, the known mechanical control means as described above has such shortcomings that, since many parts of high precision are required, the adjustments thereof are difficult, while its control range is small, and further, various troubles are liable to take place.
Accordingly, it is an object of the invention to provide a toner replenishing control device which is capable of maintaining the mixing ratio of carrier to toner in the dual or two component developing material at a predetermined constant value.
By using the photosensitive drum for a long period, there is liable to happen that the electrical characteristics of the photosensitive layer provided on the outer puriphery of the photosensitive drum are deteriorated or numerous small scratches or flaws are formed on the photosensitive layer. Therefore, it is required to periodically replace the photosensitive drum. Conventionally, various arrangements have been proposed for mounting the photosensitive drum on the copying apparatus housing without any contact with the photosensitive layer, but these known approaches have many problems such as troublesome procedures during mounting, necessity for tools, for example, a screw driver and the like, or possible damage to the photosensitive layer due to accidental contact of the photosensitive drum with the apparatus housing.
It is an object of the invention to provide a transfer type electrostatic copying apparatus in which a photosensitive drum is capable of being positively mounted to a apparatus housing through easy handling thereof.
In the heating and fixing device, the copy paper on which a toner image is formed is arranged to be passed between a fixing roller accommodating therein a heater element and a pressure roller contacting the fixing roller under pressure for fixing through the heating. In one prior art arrangement, the tip of a blade is adapted to contact the fixing roller under pressure so as to scrape off any toner adhering to the surface of the fixing roller for maintaining the surface of the fixing roller clean and also to prevent the copy paper from being wound around the fixing roller. There have been such cases that copy paper jamming takes place due to adhesion of the copy paper to the blade by residual toner stuck to the blade edge after having been removed from the surface of the fixing roller, or the copy paper is extensively soiled by the remaining toner on the blade edge or fused toner images on the copy paper sheet.
It is an object of the invention to provide a heating and fixing device for a copying apparatus for preventing a copy paper from being jammed and being soiled due to remaining toner on a blade which is arranged to prevent the copy paper from being wound around a fixing roller.